Weight reduction of automotive bodies is desired in recent years in the automobile industry from the viewpoint of preventing global warming. For instance, applying high-strength steel sheet to chassis frame parts and suspension parts can lead to thickness reduction of steel sheets and thereby contribute to weight reduction of a full vehicle.
Many of chassis frame parts and suspension parts are joined by arc welding. Welding two parts is often performed by adopting lap fillet arc welding that welds an end portion of one part of the two parts to a surface of the other part along the end portion of the one part.
In a durability test conducted on two parts fillet-welded by arc welding, a weld toe of a weld bead is a portion where cracking is prone to occur. Studies to increase fatigue strength of the weld toe have conventionally been made through various approaches including causing the weld toe to have a multilayer structure (see Japanese Laid-Open Patent Publication No. 2014-4607), studying shielding gas constituents (see Japanese Laid-Open Patent Publication No. 2012-213803), and removing a residual stress around a welded portion (see Japanese Laid-Open Patent Publication No. 10-193164). However, because those techniques increase cost due to an increase in the man-hours to weld or a need for a special gas, there is currently no means available to inexpensively increase fatigue strength without increasing the man-hours.
It could therefore be helpful to provide a lap fillet arc-welded joint that, when applied to two metal sheets to be overlapped and lap fillet welded by arc welding, exhibits favorable fatigue strength without increasing cost or the man-hours.